Immersion type heating element with a plastic head for a storage water heater tank

ABSTRACT

An improved electric immersion heater wherein the metallic heating element sheath is mechanically and electrically secured to a dielectric element head rendered conductive by suspending carbon or metallic conductors in the dielectric to produce a predetermined resistance. This allows anodic current to flow from the heating element sheath to ground when the conductor is installed in a water tank without the need for external resistors or tinning of the heating element sheath.

United States Patent 1 1 Strobach IMMERSION TYPE HEATING ELEMENT WITH APLASTIC HEAD FOR A STORAGE WATER HEATER TANK [75] lnventor: Carl G.Strobach, Clarendon Hills,

[73] Assignee: Rheem International, Inc., Chicago,

Ill.

[22] Filed: Nov. 5, 1973 [21] Appl. N0.: 412,839

[52] US. Cl. 219/336, 174/78 [51] Int. Cl. F24h 1/20 [58] Field ofSearch 219/322, 335, 336;

[56] References Cited UNITED STATES PATENTS 2,748,251 5/1956 Drugmand219/336 1 1 Jan. 14, 1975 2,947,846 8/1960 Fox 219/322 X PrimaryExaminer-J. V. Truhe Assistant Examiner-Kenneth l-lairston Attorney,Agent, or Firm-Molinare, Allegretti, Newitt & Witcoff [57] ABSTRACT Animproved electric immersion heater wherein the metallic heating elementsheath is mechanically and electrically secured to a dielectric elementhead rendered conductive by suspending carbon or metallic conductors inthe dielectric to produce a predetermined resistance. This allows anodiccurrent to flow from the heating element sheath to ground when theconductor is installed in a water tank without the need for externalresistors or tinning of the heating element sheath.

5 Claims, 6 Drawing Figures PATENIEDJANMISYS 3,860,787

I 2: I2 I i: k f II a 1 3 7 Ii H u w 7 IO.

FIG I PRIOR ART PRIOR ART FIG.3

IMMERSION TYPE HEATING ELEMENT WITH A PLASTIC HEAD FOR A STORAGE WATERHEATER TANK BACKGROUND OF THE INVENTION This invention relates toelectric heaters for water tanks, particularly an improved heatingelement head construction for an immersion heater as used in electricwater heaters.

Typical electrically heated water tanks employ an electric immersionheater. Most lined water tanks constructed of ferrous metal also containa sacrificial anode such as magnesium, aluminum or zinc. The anode is inelectrical contact with the tank and serves to cathodically protect thetank from corrosion by electrolysis.

To prevent the sacrificial anode from being sacrificed at an excessivelyrapid rate, the prior art has recognized that the uncoated coppersheathed heating element cannot be directly grounded to the ferroustank. For example, if the heating element sheath and ferrous tank are inperfect electrical contact, a substantial electropotential differencewill exist between the copper sheath and the sacrificial anode. On theother hand, it has been established that the element sheath will corrodeif the element is electrically isolated from the ferrous tank.Therefore, there must be an electrical connection between the sheath andthe tank. The amount of current flow, however, has to be controlled toprevent excessive anode depletion.

One solution employed by the art is to embed the heating element sheathin a steel head as illustrated in FIG. 2 accompanying this application.In this figure, a copper heating element sheath 7 is mechanically andelectrically secured to steel head 10 having a plastic center portion 11to retain wire leads 6. Steel head 10 is supplied with male'threads 14designed to engage the female threads in steel coupling 13 welded to thetank wall 4. To prevent excessive depletion of magnesium anode 2 due tothe intimate electrical contact between sheath 7 and tank coupling 13through steel head 10, copper sheath 7 and steel head 10 are plated witha metal 12 (thickness of metal 12 is greatly exaggerated for purposes ofillustration) of less nobility in the electropotential series thancopper such as tin. Because the gap in the electropotential seriesbetween tin and magnesium is less than the gap between magnesium andcopper and because the tin coating has the tendency to polarize, themagnesium anode will not be depleted at an excessively rapid ratedespite the fact that sheath 7 is mounted in direct electrical contactwith the tank. While this solution to the anode depletion problem issatisfactory in most cases from a technical standpoint, it requires theexpense of tin plating. Further, the tin plating may dissolve in certainwaters thereby leading to rapid anode depletion.

Another device used by the art to control excessive anode depletion isillustrated in FIG. 3. In this device, the heater head or flangecomprises copper faced steel plate 21, dielectric plate 22 and steelface plate 23. Copper face plate 21 and steel face plate 23 are not indirect electrical contact and are separated by dielectric material 22.This plate assembly or element flange is mounted on the wall 4 of watertank 1 by inserting sheath 7 through wall opening 25 and connecting theplates to the tank flange 27 through bolts 20. An insulating gasket 26separates tank flange 27 from plate 21. Electrical connection betweencopper face plate 21 and steel plate 23 is provided by a 500-600 ohmresistor. This value resistor allows sufficient current to pass from thesheath to ground (the tank) to prevent electrolytic corrosion of thesheath while at the same time preventing rapid anode deterioration.While this solution does not require the tin plating of the coppersheath, it does require a more complex heating element head and the needfor an external electrical circuit with resistor.

SUMMARY OF THE INVENTION It is an object of this invention to provide anelectric heating element for water tanks that has a conductive plasticelement head connected to the metal heating element sheath which doesnot require a less noble metal coating to prevent excessive anodedeterioration.

It is an object of this invention to provide a conductive plasticelement head for an electric water heater that does not require anexternal electric circuit to prevent excessive anode deterioration.

It is a specific object of this invention to provide a conductiveplastic heating element head that is quickly and inexpensivelymanufactured.

According to this invention, there is provided an improved all plasticheating element head for a conventional electric immersion heater havinga heating element enclosed in a metallic sheath. This improved head ismechanically and electrically secured to the metallic sheath andpreferably eliminates the need for external electric circuits or platingof the metallic sheath with a metal less noble than the sheath metalwhile at the same time controlling anode deterioration. This improvedhead comprises a dielectric solid such as a plastic resin, havingsuspended therein carbon or a metallic conductor in an amount sufficientto allow current to flow from the sheath'to ground (the tank) throughthe conductor suspended in the dielectric when the heater is installedin a water tank.

Other objects and embodiments will be found in the following moredetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side viewillustrating a conventional water tank and the placement therein of ananode and a water heating element.

FIG. 2 is a detailed sectional side view of a conventional combinationsteel and plastic element head wherein the steel portion of the head iselectrically grounded to both the metallic sheath and metallic tankcoupling thereby requiring tin plating of the copper sheath to preventexcessive anode depletion as discussed earlier.

FIG. 3 is a detailed, sectional side view of a multipiece prior artelement head or flange that requires an external electric circuit tocontrol anode depletion as discussed earlier.

FIG. 4 is a detailed partial sectional side view of the plastic elementhead of this invention as positioned in a water tank.

FIG. 5 is a detailed, sectional side view of the element headillustrated in FIG. 4 as detached from the water tank.

FIG. 6 is an end view of the heating element illustrated in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 4 and 5 illustrate theimprovement of the present invention, the prior art having beendiscussed relative to FIGS. 1 through 3. FIGS. 4 and 5 illustrate arigid plastic head 30 having intimately connected thereto a conventionaltubular, untinned copper heating element sheath 7. Tubular sheath 7houses a conventional high resistance heating wire (not illustrated)maintained in a spaced relation from the sheath 7 by a suitableinsulating material such as magnesium oxide. Head 30 is provided withsuitable male threads '33 adapted to engage the female threads in-tankcoupling 13 affixed to wall 4 of the heating tank.

As illustrated in FIG. 5, sheath. 7 is firmly embedded in plastic head30. Electrical leads 6 extend from the high resistance heating wire (notshown) in sheath 7 through non-conductive plastic center piece 35concentrically positioned within a plastic matrix 31 of head 30.Leads 6may be connected to a suitable external power source.

The portion of head 30 comprising the plastic matrix 31 is made, forexample, from a phenolic'plastic. Uniformly distributed within matrix 31are electrically conductive carbon or metallic particles 32. Thenonconductive center piece 35 is comprised of an insulator for the leads6 and preferrably is madefrom the same plastic as matrix 31. Of coursethe conductive particles 32 are excluded from center piece 35. I

The amount of particles 32 per unit volume of matrix 31 will generallydetermine the resistance of the matrix 31 of the head 30. High amountsof conductiveparticles 32 generally result in lower resistance and loweramountsresult in higher resistance. Alternatively, par ticles 32 cancomprise discrete conductive-units dispersed in a polymerized resin,each discrete unit comprising an aggregate of conductive particlesbonded together by the resin matrix 31. Conductive resins comprisingconductive carbon or metallic particles suspended in a resin matrix arewell known to those trained in the art and need not be described indetail herein. See for example US. Pat. No. 3,056,750.

In general, any type of solid resin of either an inorganic or organicnature, natural or synthetic, which is capable of serving as adielectric material may be used in the practice of the presentinvention.

Preferably, the matrix 3l-particle 32 combination has a resistance valuesufficient to allow a small amount of current to flow from the sheath 7to the tank so as to eliminate the need for tinning the copper sheath 7or using an external resistance. Typically, the matrix 31- particle 32combination has a resistance of about 500-600 ohms although a resistancerange of 20010 1,000 ohms has been found satisfactory.

The resin for matrix 31 used must have sufficient stability to standexposure to water temperatures on the order of l00-l 80 F. asencountered in ordinary water heaters. f

A preferred resin would'be a single stage phenolic compound with fillersadded to improve resistance to temperature, cracking, chemicals, etc.

The conductive particles suspended in the dielectric matrix consist ofeither carbon particles or metal particles or a mixture of both.Accordingly, any metal powder may be used as the conductive material ofthe present invention, such as,'for example, copper, iron, zinc,aluminum, magnesium, tin, antimony, silver, chromium, etc. In addition,conductive oxides of metals may be'used. I

With respect to carbon, certain forms offer lower resistance values,such as crystalline carbon (graphite), whereas the amorphous forms ofcarbon (carbon black) afford higher values of resistance. Lamp black,having-a specific resistance less than carbon black and greater thangraphite may be used to obtain resistances of an intermediate value.

The invention is therefore defined and limited only by the followingclaims.

I claim as my invention:

1. In an electric immersion water heater element for a water heater tankwhich includes a heating element enclosed in and electrically insulatedfrom a metallic sheath, and an element head for attachment to a waterheater tank with the heating element adapted to project to the interiorof the water heater tank said element head being mechanically andelectrically secured to the metallic sheath, the improvement whichcomprises an element head including a dielectric solid portion incontact with said sheath and to contact said tank, said dielectricportion having suspended therein conductive carbon or metallic particlesin an amount sufficient to allow current to flow from said sheaththrough the dielectric portion to ground onsaid tank, said head alsoincluding a nonconducting portion through which external leads areprovided for connecting said heating element to a power source. I j

2. An electric immersion heater according to claim 1 wherein theheating-element comprises an untinned copper sheath and said headcontains a carbon or metallic conductor in an amount sufficient toeliminate said tinning without the necessity'of an' external resistor.

3. An electric immersion heater according to claim 1 wherein the carbonor metallic conductor is present in an amount sufficient to provide aresistance of ZOO-1,000 ohms between the sheath and ground.

4. An electric immersion heater according to claim 1 wherein said solidportion is a plastic resin.

5. An electric immersion heater according to claim 1 wherein saidnonconducting portion comprises a plastic resin concentricallypositioned with the dielectric portion. 1

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3.860.787Dated Januarv 14 1975 Inventor(s) Carl G. Strobach It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover sheet, Item (73) Assignee should read:

-- Rheem Manufacturing Company, New York, New York Signed and Sealedthis Seventh Day Of February I 978 [SEAL] A ttest:

RUTH C. MASON LUTRELLE F. PARKER Attesting Officer Acting Commissionerof Patents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3 860 787 Dated Januarv 1Q, 1975 Inventor(s) CarlG. Strobach It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet, Item (73) Assignee should read:

-- Rheem Manufacturing Company, New York, New York Signed and Sealedthis Seventh Day Of February I978 [SEAL] A ttesl:

RUTH C. MASON LUTRELLE F. PARKER Arresting Officer Acting Commissionerof Patents and Trademarks

1. In an electric immersion water heater element for a water heater tankwhich includes a heating element enclosed in and electrically insulatedfrom a metallic sheath, and an element head for attachment to a waterheater tank with the heating element adapted to project to the interiorof the water heater tank said element head being mechanically andelectrically secured to the metallic sheath, the improvement whichcomprises an element head including a dielectric solid portion incontact with said sheath and to contact said tank, said dielectricportion having suspended therein conductive carbon or metallic particlesin an amount sufficient tO allow current to flow from said sheaththrough the dielectric portion to ground on said tank, said head alsoincluding a nonconducting portion through which external leads areprovided for connecting said heating element to a power source.
 2. Anelectric immersion heater according to claim 1 wherein the heatingelement comprises an untinned copper sheath and said head contains acarbon or metallic conductor in an amount sufficient to eliminate saidtinning without the necessity of an external resistor.
 3. An electricimmersion heater according to claim 1 wherein the carbon or metallicconductor is present in an amount sufficient to provide a resistance of200-1,000 ohms between the sheath and ground.
 4. An electric immersionheater according to claim 1 wherein said solid portion is a plasticresin.
 5. An electric immersion heater according to claim 1 wherein saidnonconducting portion comprises a plastic resin concentricallypositioned with the dielectric portion.